A major irritation for those of us who take seriously the menace of Islamist terrorism is the tendency of members of the chattering classes to say brightly, "Oh, it's the Christian right that worry me." You might as well compare a Bengal tiger to an ill-tempered moggie, writes Ruth Dudley Edwards

Sociologist Prof Steve Bruce feels the same. Although he has been a long-time sympathetic student and chronicler of Dr Ian Paisley, he feels in retrospect that he was a bit harsh. "Increasing awareness of what a real jihad looks like," he tells us, "made me much more aware of the relatively constrained nature of Paisleyism." Paisley may denounce from his altar the shocking carry-on of the ungodly, but his followers know that it would be a grievous sin to act violently towards an immodestly dressed young woman. As Bruce here demonstrates convincingly, like most evangelical Protestants, Paisley and his followers would like to convert people to their way of thinking, but they fully accept the principles of liberal democracy and are not in the business of waging holy war. For instance, while Free Presbyterians may fight politically to have a village kept dry or a park closed on Sunday, they accept the democratic decisions of local councils. Loyalist paramilitaries are secular in their attitudes and their crimes are unequivocally condemned by the religious.

We have been lazy in the South about trying to understand the culture of our Protestant neighbours: it suited us to view their antipathy to Roman Catholicism as nothing but bigotry. Yet from the perspective of many of them, not a lot has changed since the Reformation challenged a corrupt and authoritarian church which subsequently took every opportunity to persecute Protestants. The special circumstances of Northern Ireland have reinforced that belief: most Protestants think (with some justification) that there were plenty of Irish priests with a sneaking regard for IRA terrorists.

TO FUNDAMENTALISTS LIKE Paisley, Roman Catholicism is both a false religion and the source of innumerable social vices. Bruce sums up the very common Ulster Protestant view (which, though dated, is not unfounded) that while they "are self-reliant, hard-working, diligent, honest, loyal, responsible, and temperate", Catholics "are discouraged from thinking for themselves by priests who wish to keep their people in a state of dependency . . . are slothful, dishonest, and untrustworthy", owe a higher loyalty to Rome than to their own country, are sexually irresponsible and fritter away their earnings on gambling, smoking and alcohol before running off to confession to wipe the slate clean. What's more, priestly celibacy encourages sexual perversion.

Ulster Protestants are mostly polite people who wouldn't say such things out loud, but Paisley delighted in shouting about it publicly. Since he takes the Bible literally, it made perfect sense to use Old Testament language to describe the church against whose manifold errors it was his duty to protest. He would not have set out deliberately to upset his Catholic neighbours by describing Rome as Babylon or the Great Whore, but his duty was clear: the truth is the truth and must be proclaimed regardless of the consequences. Nor was he much less offensive in his assaults on the mainstream Protestants he dubbed apostates.

The problem for Northern Ireland was that Paisley was not some two-bit preacherman. Gifted, charming, charismatic and ferociously energetic, he had a profound effect on the conduct of public life. Even though I go a long way with Bruce and accept that Paisley always denounced violence, I still believe that his vanity, his craving for the spotlight, a messianic conviction that his is the only true path, his tendency to wash his hands when he has got people over-excited, parochialism, paranoia and intellectual tunnel vision have frequently had a malign and divisive influence on public life in Northern Ireland.

The sheer offensiveness of his denunciations of religious and political opponents had much to do with his desire to attract attention: it was unnecessarily unmannerly of him to denounce a priest by telling him to go back "to your priestly intolerance, back to your blasphemous masses, back to your beads, holy water, holy smoke and stinks and remember we are the sons of the martyrs whom your church butchered and we know your church to be the mother of harlots and the abominations of the earth".

BRUCE'S BOOK IS not an easy read, but it is very enlightening. Quite apart from elucidating much that is perplexing about Paisley's career, it also explains why someone whose church has only around 12,000 members and who as a politician has so often been written off by commentators and politicians as "an oaf, a charlatan, or a buffooon", has ended up cock of the political walk. Paisley appealed to a besieged people's need to feel part of a religious and political heritage. Unlike middle-class unionist leaders he had no truck with cosmopolitanism, he is seen as embodying classic Protestant virtues and, most of all, there is the oft-repeated mantra: "You know where you are with the Doc". Whether his electorate now feel that as they see him grinning alongside Martin McGuinness is another story. By forcing him to quit as Moderator, his flock made it clear they did not.